Action! is an Atari-specific programming language written by Clinton Parker and sold by Optimized Systems Software (OSS) in ROM cartridge form starting in August 1983. It is the only language other than BASIC and assembler) that had real popularity on the platform and saw any significant coverage in the Atari press; type-in programs and various technical articles were found in most magazines. In comparison, languages like Forth and Logo saw much less use and almost no press coverage.

Reviewers at the time gushed about the system. They noted that practically every aspect was superior to anything available at the time; compiling was almost instantaneous, the resulting code ran almost as fast as hand-coded assembler, the full-screen editor was universally loved, and the entire system took up only 8k due to clever memory management. The only complaint, also universal, was the poor quality of the original manual set.

Action! uses a greatly cut-down version of the ALGOL syntax, and thus bears strong similarities with Pascal and C, which were also derived from ALGOL. Like those languages, Action! is procedural, with programs essentially consisting of a large collection of functions that call each other. It lacked encapsulation or data hiding, but that is not a serious concern in the limited program sizes available on an 8-bit machine. Syntactically it looks very similar to Pascal, with the exception that it uses ALGOL 68 DO/OD style bracketing rather than Pascal's BEGIN/END.

Action! included a number of features to allow it to run as fast as possible. Notably, it's main data types were BYTE, INT and CARD, 8-bit and 16-bit signed and unsigned values, respectively. These map directly onto the basic 6502-types. The language also included a syntax to directly refer to these objects in memory so they could be mapped into hardware registers. For instance, one could set a variable to BYTE RTCLOK=20 which defined the 8-bit value at memory location 20 to be the value of the real-time clock. The user could then read or write to that register using the name RTCLOK.

Action! had a number of limitations, none of them very serious. Variables were assigned to memory in procedures, not on a stack, so recursion was not supported internally. Curiously, Action! did not include support for floating point types, although such support is built into the machine's OS ROM (see Atari BASIC for details) and available to any programming language. This is a significant limitation in some roles, although perhaps not for its target market. It also lacked most string handling, but made up for this somewhat with a series of PRINT commands that made formatted output easy.

Generally, Action! programs had performance on-par with reasonable-quality assembler, while being much easier to program. In one review, it ran Byte's Sieve of Eratosthenes 219 times faster than Atari BASIC, while its source was only a few lines longer. In comparison, the assembler version's source ran on for several pages. Such performance, combined with terse code and library functions to access much of the platform's hardware, made it suitable for action games while still having a simple source format suitable for type-in programs. It deserved to be much more popular, and may have been had it been released earlier, or by Atari itself.

Action! inspired several similar languages that differ largely in syntax and various features that they do or do not support. Examples include PL65 and Quick.

The ; is a comment marker, which was a commonly used as the comment marker in assembler as well. The PROC is the start of a PROCedure, which ends (perhaps oddly) with RETURN. In Action!, the last PROC in the program is the one that runs first, in this case "Hello". This is something of a mix between Pascal where the "global code" defines the program entry point, and C, where the function called "Main" is the entry point. The only line of code in this example is PrintE, which simply prints a string, while the more common PrintF is a formatted print similar to printf in C.

Like assembler, it was common for variables to be specified at a particular address that mapped onto one of the Atari's "shadow registers" that were used to communicate between the hardware and user programs. Here is a simple variation on Hello World that demonstrates this concept, as well as a basic loop:

; Hello world in a loop
PROC Hello()
BYTE RTCLOK=20, ; decimal address of system timer
CONSOL=$D01F ; hex address of the key-pressed register
CARD TIME
RTCLOK=0 ; reset the clock
WHILE CONSOL>6 ; did the user press a key?
DO
PRINTE("Hello World!")
OD
TIME = RTCLOK
PRINTF("Ran for %E %U jiffies",TIME)
RETURN

Note that the definitions of RTCLOK and CONSOL are not setting the values, but stating that they are at those memory locations. The syntax changes when those variables are accessed; the RTCLOK=0does set the value of that location. Also notice the syntax of loops, which work similarly to Pascal's BEGIN/END but use DO/OD.

There is a clever trick in this code. Note that RTCLOK is defined as a BYTE but TIME is defined as a CARD, a 16-bit value. This is because the clock value is stored in three bytes, 18, 19 and 20. By defining TIME as a CARD, when that value is read it automatically reads two bytes, thereby getting a value from both 20 and 19. This solution ignores the third byte, but since the value is from 0 to 65535 jiffies, about 36 minutes, this can safely be ignored for a program that is likely to run for a few seconds. This solution avoids the need to read two bytes and manipulate them into a 16-bit value, something that is commonly found in BASIC programs.

Action_manual_3rd-revised_edition_2015_by_GBXL.pdf ;The complete Action! manual! Editor, Monitor, Language, Compiler, Library, Run Time, Toolkit. 3rd revised edition 2015 by GoodByteXL. Highly recommended by the AtariWiki! This is, without any(!) doubt, the very best edition worldwide available. Nobody does it better. Mega-thanks to GoodByteXL for this outstanding work and the many hours of work to the community. We are deep in your debt! Thank you so much. :-)))

ACTION.XEX ; Thanks goes to Peter Dell for making the XEX-file out of the above source code. Peter, we owe you so much, please go ahead! :-)

Action_Editor-MADS.xex ; If you rename the file to E.COM, you can even use it under SpartaDOS I for example with D1:E MYSRC.ACT to direct load the MYSRC.ACT file into the editor. Further, this editor can even be used for BASIC, PASCAL, FORTH etc... A Giga-thanks goes to Alfred from AtariAge for extracting the source code from Clinton Parker's original source code and JAC! from AtariAge for building the xex file from that very source code, while adapting to MADS. Great job, not only for Action! :-)))